Giải Bài tập 5 trang 56 Toán 11 tập 1 Chân trời

a) $\left\{\begin{matrix}u_{3}-u_{1}=20\\u_{2}+u_{5}=54\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}u_{1}+2d-u_{1}=20\\u_{1}+d+u_{1}+4d=54\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}d=10\\u_{1}=2\end{matrix}\right.$

b) $\left\{\begin{matrix}u_{2}+u_{3}=0\\u_{2}+u_{5}=80\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}u_{1}+d+u_{1}+2d=0\\u_{1}+d+u_{1}+4d=80\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}2u_{1}+3d=0\\2u_{1}+5d=80\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}d=40\\u_{1}=-60\end{matrix}\right.$

c) $\left\{\begin{matrix}u_{5}-u_{2}=3\\u_{8}.u_{3}=24\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}u_{1}+4d-u_{1}-d=3\\(u_{1}+7d)(u_{1}+2d)=24\end{matrix}\right.$

$\Leftrightarrow \left\{\begin{matrix}d=1\\u_{1}=1\end{matrix}\right.$ hoặc $\left\{\begin{matrix}d=1\\u_{1}=-10\end{matrix}\right.$